Changing the baud rate of HC-05 bluetooth module to work with MultiWii.

13 Jul 2015

HC-05 is cheap yet capable and easy to use Bluetooth SPP (Serial Port Protocol) module and it can be used to control your
quadcopter which runs MultiWii. There is one catch though. Default Baud rate of HC-05 is 9600 and that’s a problem, because
MultiWii software expects serial input-output device to operate at 115200. Gladly it’s fairly easy to change Baud rate of HC-05
if you have USB-TTL adapter or Adruino. In this post I’ll show how to change Baud using USB-TTL adapter.

How to connect with FTDI

At first we need to connect HC-05 with USB-TTL adapter. Connect your HC-05 to match the table below:

HC-05

USB-TTL adapter

TXD

connect to

TXD

RXD

connect to

RXD

GND

connect to

GND

VNC

connect to

+5

How to get to the AT mode

At first we need to find out which type of HC-05 breakout you have: with or without “switch” button. If you have HC-05
with “switch” button then to enter AT mode just press and hold “switch” button before powering USB-TTL adapter. HC-05 will
slowly blink every 2 seconds to indicate that it’s in AT mode. If there is no “switch” button you’ll need to hot wire PIN
#34 on HC-05 before powering USB-TTL adapter. And again after powering HC-05 will slowly blink every 2 seconds to
indicate that it’s in AT mode.(I’ve used second method before I realized that my HC-05 actually had “switch” button for that)

To summarize this are the steps to enter into AT mode:

First way (if you have “switch” button on your HC-05)

Step 1: Press and hold “switch” button

Step 2: Supply power to USB-TTL. Then the HC-05 will enter to AT module.

Second way (if you don’t have “switch” button on your HC-05)

Step 1: Connect PIN34 to the power supply PIN(VCC).

Step 2: Supply power to USB-TTL (the PIN34 is also supplied with high level since the PIN34 is connected with
power supply PIN). Then the HC-05 will enter to AT module.